This invention relates to articles that can be applied to surfaces to reduce the drag caused by fluids (e.g., air, gas, water, etc.) flowing across such surfaces.
It is desirable to reduce the drag caused by bodies passing through fluid media, such as an airplane moving through air, a boat moving through water, or a motor vehicle moving through air. Relatively small reductions in drag can significantly reduce the fuel needed to propel the body. Improved fuel economy can result.
To enhance their utility, drag reduction articles should possess certain properties. For example, they should be weatherable. That is, the drag reduction articles should not deteriorate or lose performance as a result of exposure to ultraviolet radiation, wind, sand, rain, snow, ice, repeated and substantial changes in temperature, etc. Further, the drag reduction article should adhere well to the exterior of the vehicle to which it is applied, e.g., an aircraft, and should have resistance to fluids to which it might be exposed to, e.g., organic solvents. A certain degree of conformability is also desired to facilitate application to flat surfaces or smooth contoured ones, i.e., those essentially free of surface protrusions, such as raised rivets. For some applications, the drag reduction article should remove cleanly and easily from a surface to which it has been applied. Finally, it is desirable that the drag reduction article be easily produced, for example, by minimizing the number of layers in its construction. By minimizing the number of layers required for a drag reduction article, its cost of manufacture can also be decreased.
Various drag reduction articles are known and comprise a thermoplastic or thermoset polymeric film having a patterned surface that reduces drag. Examples of these articles can be found in U.S. Pat. Nos. 4,986,496; 5,069,403; and 5,133,516, each to Marentic et al. The articles of Marentic et al. usefully reduce drag. Another example of drag reduction articles can be found in U.S. Pat. No. 5,848,769 to Fronek et al. The articles of Fronek et al. improve upon those of Marentic et al. by providing improved handling, removability, and weathering characteristics while usefully reducing drag.